Eggs have long been considered to be among the most nutritionally valuable of foods for human consumption. Egg protein is of exceptional nutritional quality and is, in fact, used as a standard against which the nitritional efficiency of other food proteins are evaluated. Egg protein is found in both the white portion of the egg and in the yolk. Fat and cholesterol, however, are concentrated in the yolk. According to Composition of Foods, Agricultural Handbook No. 8, U.S. Department of Agriculture (1963), 100 grams of whole egg provides about 4 grams of saturated fat and 550 mg. of cholesterol.
It is now generally believed that high blood cholesterol levels in humans are implicated in the onset and/or severity of cardiovascular disease. The amount of saturated fat ingested is also, in some manner, believed to be a factor in promoting the development of elevated blood cholesterol levels. Polyunsaturated fat, i.e., linoleic acid, on the other hand, is considered to be effective in lowering cholesterol levels. With the emphasis now being placed on the importance of reducing the dietary intake of cholesterol and saturated fat, many medical and nutrition authorities recommend that the intake of a number of highly popular foods, including eggs, be restricted or that their use be eliminated entirely, in some instances. There is evidence that egg yolk cholesterol may be particularly effective in increasing the levels of cholesterol in the blood. As a result, many people have been required to reduce drastically the number of eggs in their diets and are thus deprived of foods which have traditionally been considered among the most enjoyable and nutritious.
There are a number of patents which are directed to providing egg products with organoleptic characteristics similar to whole eggs but having reduced calorie content and/or cholesterol levels. Exemplary of such patents are U.S. Pat. No. 3,207,609 to Gorman et al., U.S. Pat. No. 3,475,180 to Jones, and U.S. Pat. No. 3,563,765 to Melnick.
In order for a low cholesterol liquid egg product to be acceptable to the consumer, however, it must be substantially similar to whole eggs with respect to functional and organoleptic properties such as color. Color is extremely important, because it is the first impression imparted to the consumer, and, if such is not satisfactory, the possibility of acceptance of the egg product will be greatly diminished even though the other organoleptic and functional properties are satisfactory. Not only must the color of a low cholesterol liquid egg product be similar to raw whole eggs, but also, when the product is cooked, the color must be similar to that of cooked whole eggs, and, when the product is used for preparing cakes, it must impart to these products substantially the color normally imparted by whole eggs. U.S. Pat. No. 3,840,683 to Strong et al. ("Strong '683") discloses one technique by which the characteristic color of whole eggs is imparted to a cholesterol-free egg product (comprising egg whites, nonfat milk solids, and vegetable oil) with a mixture of beta-carotene and an extract of plant xanthophylls.
In order to prevent spoilage or microbiological growth, it is desirable to freeze the low cholesterol egg product for the purposes of storage and distribution. In the frozen state, the product will have a shelf life of about one year, allowing for orderly manufacturing, testing, storage, distribution, and marketing. If the product were refrigerated and not frozen, the shelf life would be about one week, a period of time too brief to allow for current distribution and marketing practices.
Consumer acceptability of low cholesterol egg products also requires that such products have acceptable organoleptic properties after freezing and thawing. However, many such products subjected to this sequence of steps tend to separate into two distinct layers. The top layer will be opaque, while the bottom layer will be relatively clear. The degree to which separation occurs is a measure of the freeze-thaw stability of the product. It is, of course, desirable that a low cholesterol egg product has a relatively high degree of freeze-thaw stability so that little or no separation occurs upon thawing, thereby enabling the consumer to use the thawed product directly without mixing. The viscosity of a low cholesterol liquid egg product should be substantially similar to that of whole fresh eggs, and the texture of the egg product when cooked (e.g., scrambled) should also be substantially the same as that of the cooked whole eggs. U.S. Pat. No. 3,911,144 to Strong et al. ("Strong '144") discloses one approach for producing a substantially cholesterol-free liquid egg product with a relatively high degree of freeze-thaw stability which involves incorporating xanthan gum in the product.
It has also been desired to incorporate vegetables in low cholesterol liquid egg products for preparation of a low cholesterol vegetable omelette mix. However, this has not been possible, because it was feared that the vegetables would contaminate the liquid egg product with microorganisms. Consequently, low cholesterol vegetable omelette mixes have not been commercially available, and, instead, consumers themselves have had to add vegetables to available low cholesterol liquid egg products at the time when they wish to make a vegetable omelette.